The Pacers can't beat Miami. They just have no chance in hell. Roy Hibbert is simply too slow and limited defensively to make a competent team defense against Miami's skilled speed and size.
The Knicks might be able to but that depends a lot on Raymond Felton showing up for the playoffs. Last two go-arounds he was a no-show. Can't beat Miami being this dependent on Carmelo. They need other guys to step up and provide some more balanced scoring. Felton's dribble penetration is key to that.
Chicago has a chance too. Their rebounding, defense and size cause Miami issues. I don't have much trust in their offense with Derrick Rose leading the charge. I think Rose is too easy for LeBron to contain. But guys like Joakim Noah can do a lot of damage.
I still think Boston has the best chance in the East of knocking the Heat off. Their inability to contain Rondo. Garnett's defensive quality and mobility. Encouraging signs of Bradley being able to slow down Wade. LeBron will go off in a ridiculous way but they might be able to slow down the rest of them enough to take them out.